Threat Descriptons



Category :


Type :


Aliases :



This is a group of viruses that are very similar in structure. The virus family is known as Moose. There are four known variants, all of which contain the word 'Moose' in the code. The viruses also contain a version number, much like the Yankee Doodle family.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical Details

All viruses in the Moose family infect program files by appending the viral code to the original file. Different variants infect different types of files, either COM, EXE or SYS. When the virus infects a SYS file it overwrites the file's header information. Infected SYS files crash the computer.

Moose viruses are not memory-resident. They only infect files when run. The virus tries to find a suitable program in the current directory, and if there are no files to infect, it switches one level up and tries again. It repeates this until it reaches the root directory of the drive.

When a suitable file is found, Moose appends its code in the file and modifies the entry point of the file. Besides this Moose may change one byte somewhere in the host file.

The result of this one-byte corruption is always unknown. Usually it does not affect the program in any way but sometimes it causes the program to crash at runtime. The virus uses the computer's real time clock to decide whether to corrupt a byte in the host file or not. In most cases the corrupted program is not repairable. It has to be restored from a backup copy or the original setup media.

The Moose viruses were found in Gothenburg, Sweden in 1993. They were discovered at the local university which may mean that the author was a student at the university.

More Support


Ask questions in our Community .

User Guides

Check the user guide for instructions.

Contact Support

Chat with or call an expert.

Submit a Sample

Submit a file or URL for analysis.